It is known that a metallic gasket comprises an elastic metallic plate on which beads are formed, the joint surfaces of a jointed member being efficiently sealed by the beads. This metallic gasket is inserted between, for example, the joint surfaces of a cylinder head and a cylinder block of an internal combustion engine, and seal lines are formed on the joint surfaces by the tightening forces of bolts, thereby enabling sealing of portions to be sealed.
Such a metallic gasket is previously disclosed in, for example, Japanese Patent Application No. 57-81530 filed by the applicant of the present invention. The metallic gasket disclosed in this prior application includes beads each having a bead width sufficiently greater than its bead height and a base plate having surfaces which are covered with a sealing material or the like by surface treatment, the sealing being realized by a single base plate.
As shown in FIG. 3, a metallic gasket 2 of this conventional type is illustrated and includes beads 10 which are formed to surround individual combustion chamber holes 6 to be sealed. The beads 10 meet between adjacent ones of the combustion chamber holes 6, and often form a junction 12. At the junction 12, a plurality of beads 10 meet, with the result that a bead width L.sub.1 at the junction 12 becomes greater than a bead width L.sub.2 at a non-junction 14. Since, in this manner, the bead width is made greater than the bead height at the junction 12, the spring constant of the junction 12 becomes smaller than the spring constant of the non-junction 14. This causes a reduction in sealing pressure at the junction 12, thus resulting in various problems such as the non-uniformity of sealing pressure acting upon the joint surfaces.
For this reason, there is an instance wherein gas or oil leaks from a periphery of the junction 12 at which sealing pressure is weakened. In order to ensure the sealing property of the junction 12 at which sealing pressure is weakened, a great fastening force must be made to act upon this junction 12. As a result, an excessive fastening force acts upon the non-junction 14 and can cause cracks to be formed in the bead, and this raises the problem of a reduction in sealing property.
It is, therefore, an object of the present invention to provide a metallic gasket in which it is possible to eliminate or at least minimize the non-uniformity of sealing pressure acting upon a joint surface by the prevention of a reduction in sealing pressure at each junction at which sealing beads meet, thereby achieving more effective sealing.
To this end, in accordance with the present invention, there is provided a metallic gasket comprising an elastic metallic plate having beads formed thereon, the beads being formed on the elastic metallic plate so that the bead width at each junction at which each bead meet an adjacent bead may be made approximately equal to the bead width at each non-junction.
In accordance with the construction of the present invention, beads for sealing portions to be sealed are formed so that bead width at each junction may be made approximately equal to bead width at each non-junction. Therefore, the spring constant of each of the junctions does not become smaller than that of each of the non-junctions. Accordingly, it is possible to prevent a reduction in sealing pressure at the junctions and hence the occurrence of non-uniform sealing pressure.